1. Field of the Invention
The present invention relates to a mobile communication (or communications) terminal such as a cellular (or mobile) phone for showing map data in accordance with position data, and relates to a map display system including the mobile communication terminal and a server for storing map data.
Priority is claimed on Japanese Patent Application No. 2004-186370, filed Jun. 24, 2004, the content of which is incorporated herein by reference.
2. Description of Related Art
FIG. 9 is a block diagram showing a conventional map display system using a cellular phone, FIG. 10 is a flowchart showing the operation of this system.
With reference to these figures, the cellular phone 10 having a GPS (Global Positioning System) function acquires and communicates with GPS satellites 20, and computes data of the present position (i.e., the present position data). The cellular phone 10 then confirms whether it is possible to access a map data service server 40 via a wireless base station 30. If it is possible, the cellular phone 10 determines whether map data corresponding to the position data is stored in a database of the map data service server 40. If corresponding map data is stored, the cellular phone downloads and displays the data. In addition, the database of the map data service server 40 also stores data for route search or route guidance based on position data and destination data, and similarly, the stored data can be appropriately downloaded in accordance with movement of the cellular phone 10.
In addition, there are known devices or systems such as (i) a portable terminal for implementing a navigation function without using a position detection device (see, for example, Japanese Unexamined Patent Application, First Publication No. 2004-028837), (ii) a navigation system having no storage medium for map data (see, for example, Japanese Unexamined Patent Application, First Publication No. H10-197258), and (iii) a navigation system performing route guidance data retrieval by using a portable communication device in a standby state (see, for example, Japanese Unexamined Patent Application, First Publication No. 2002-328042). Typically, portable terminals used in the conventional navigation systems use an electronic compass having a geomagnetic sensor in order to measure a direction or an azimuth.
In the conventional map display system shown in FIG. 9, for the cellular phone 10 to obtain and display map data or route data from the map data service server 40, the cellular phone 10 must be present within the service areas of the wireless base stations 30. Generally, positional detection using the GPS function should be possible in an open air environment (such as on the top of a mountain) where signals from the GPS satellites 20 are acquirable. However, in mobile communication, each service area is generally defined in a place having a large population (i.e., having a large number of buildings where signals from the GPS satellites 20 cannot be easily acquired), and in most cases, the mobile communication service cannot be used in a place such as the top of a mountain (where signals from the GPS satellites 20 can be easily acquired). In addition, signals from the GPS satellites 20 may be acquired in foreign countries. However, some mobile communication service providers do not provide service in foreign countries, and in this case, map data or route data cannot be obtained from the map data service server 40.